Confirming the expression of DRRGs in OSC
At first, we download the expression profiles of 379 OSC patient tissue samples based on TCGA database, and the datasets of 88 normal ovary tissue samples based from GTEx database (Fig. 2A-B). PCA analysis indicated that OSC (blue) and normal (red) tissues could be well discriminated by the expression profiles of these DRRGs (Fig. 2C). Moreover, we found the expression of MCM5, POLD2 and RPA1 was not significantly changed in OSC samples compared to normal ovary samples, the level of ORC2/4, LIG1, RNASEH2B/C, RFC1, POLE4 and POLD4 was significantly decreased in OSC, but other DRRGs was obviously increased in OSC samples compared to normal samples (Fig. 3). These results suggested the aberrant DNA replication was played a key role in the development and progression of OSC.
DNA alteration of DRRGs in OSC
Subsequently, we detected the DNA alteration level of these DRRGs in OSC based on cBioProtal database. The OSC dataset suggested DNA alteration percentages of these DRRGs were 4% (POLA1), 2.9% (POLA2), 1.3% (PRIM1), 1.6% (PRIM2), 2.3% (POLD1), 2.6% (POLD2), 12% (POLD3), 5% (POLD4), 2.9% (POLE), 1.9% (POLE2), 1.3% (POLE3), 2.6% (POLE4), 6% (ORC1), 4% (ORC2), 2.6% (ORC3), 1.9% (ORC4), 4% (ORC5), 1.6% (ORC6), 6% (MCM2), 3% (MCM3), 6% (MCM4), 1.9% (MCM5), 1.3% (MCM6), 3% (MCM7), 2.6% (RFC1), 4% (RFC2), 2.3% (RFC3), 23% (RFC4), 1.6% (RFC5), 2.3% (RPA1), 1.6% (RPA2), 3% (RPA3), 1.6% (RPA4), 3% (DNA2), 1.6% (FEN1), 1.6% (LIG1), 5% (RNASEH1), 12% (RNASEH2A), 3% (RNASEH2B), 2.9% (RNASEH2C), 1.9% (CDC6), 8% (PCNA), and 5% (CDT1) (Fig. 4A). These DRRGs alteration were primely enriched in amplification in OSC patients (Fig. 4B), which partly explained the upregulation of DNA replication in OSC. However, the survival analysis indicated that the prognosis was not correlated with the DNA alteration of DRRGs (Fig. 4C).
Function of these DRRGs in OSC
We constructed the three-dimensional structure of key DRRGs in DNA replication via the PDB database. The result showed that ORC complex, MCM complex, CDC6 and CDT1 could directly interacted with each other, which binds to DNA to activate replication. Moreover, RFC1-5 directly interact with PCNA to accelerate the extension of DNA (Fig. 5A). We also made a correlation analysis among these DRRGs in normal ovary, OSC, and normal ovary plus OSC datasets based on TCGA and GTEx database. The stratification and clustering of these DRRGs was markedly observed in OSC dataset and normal ovary plus OSC datasets, but the level of DRRGs were not significantly correlated with each other in normal ovary (Fig. 5B), indicating the level of DNA replication might be obviously enhanced in OSC by the mutual feedback regulation in these DRRGs. We further constructed the PPI network for these DRRGs based on GeneMANIA database, including RNASEH2C, POLE4, RNASEH1, RNASEH2B, RPA4, DNA2, RFC1, POLD3, RNASEH2A, ORC6, PRIM2, POLE3, POLA2, ORC4, RFC5, POLE, POLE2, POLD4, ORC5, LIG1, POLA1, PRIM1, RFC2, CDT1, ORC2, RFC3, ORC3, POLD1, POLD2, FEN1, RFC4, MCM4, ORC1, MCM5, MCM6, MCM7, MCM2, CDC6, MCM3, PCNA, RPA2, RPA3, RPA1, CDC45, DBF4, CDC7, MCM10, CLSPN, MCM8, ATRIP, GINS2, GINS4, GINS1, RAD9B, RAD1, RAD17, HUS1, GMNN, POLB, CDK2, RAD9A, PPIA and RAD52 (Fig. 5C).
Further GO enrichment analysis indicated that these genes were significantly enriched in cellular process, metabolic process, response to stimulus, cell proliferation, reproductive process and immune system process in Biological process term, remarkedly enriched in cell part, protein-containing complex, cell junction, nucleoid, and supramolecular complex in Cellular component term, signally enriched in binding, catalytic activity, molecular function regulator, and transcription regulator activity in Molecular function term (Fig. 5D).
The effect of DRRGs on signaling pathways
KEGG enrichment analysis indicated that these genes were enriched in DNA replication, nucleotide excision repair, mismatch repair, cell cycle and base excision repair (Fig. 6A). All the DRRGs promote DNA replication was shown in Fig. 6B, which is the classical molecular function for these DRRGs. RFC1-5, PCNA, RPA1-4, POLD1-4, and LIG1 were involved in mismatch repair progression (Fig. 6C). Both RPA1-4, POLD1-4, POLE1-4, RFC1-5, PCNA and LIG1 played key roles in nucleotide excision repair progression (Fig. 6D). POLE1-4, POLB, POLD1-4, PCNA, FEN1 and LIG1 were enriched in base excision repair (Fig. 6E). ORC complex, MCM complex, CDK2, PCNA, CDC6, CDC45, CDC7, and DBF4 were involved in the progression of cell cycle (Fig. 6F). These results indicated that DRRGs have an important function in genome stability.
Analysis of DRRGs expression identifies two distinct subgroups of OSC
Next, we used consensus clustering analysis to classify OSC tissue samples into different DRRG patterns, and two distinct DRRG clusters were identified using unsupervised clustering (Fig. 7A). Two cluster group have significantly differently expressed genes (Fig. 7B). Hence, we extracted these differently expressed genes by Volcano maps (Fig. 7C) and heat maps (Fig. 7D). KEGG enrichment analysis indicated that these differently expressed genes were remarkedly involved in p53 signaling pathway, pyrimidine metabolism, purine metabolism, progesterone mediated oocyte maturation, platinum drug resistance, and mismatch repair (Fig. 7E). GO enrichment analysis found that these differently expressed genes were significantly enriched in spindle organization, sister chromatid segregation, regulation of mitotic cell cycle phase transition, regulation of cell cycle phase transition, and DNA replication (Fig. 7F).
Furthermore, we found m6A methylation related genes were significantly increased in cluster 1 group compared to cluster 2 group, including, METTL3, METTL14, WTAP, VIRMA, RBM15, RBM15B, YTHDC1, YTHDC2, YTHDF3, YTHDF1, YTHDF2, HNRNPC, IGF2BP1, IGF2BP2, IGFBP3, RBMX, HNRNPA2B1, FTO and ALKBH5 (Fig. 8A). The ferroptosis related genes was significantly and differently expressed in cluster 1 compared to cluster 2, especially in HSPA5, NFE2L2, HSPB1, FANCD2, FDFT1, SLC1A5, TFRC, RPL8, NCOA4, LPCAT3, GLS2, CS, CARS, ALOX15, ACSL4 and AIFM2 (Fig. 8B). Immuno-infiltration analysis suggested that CD4 T cell was highly infiltrated in cluster 1, but CD8 T cell, and Myeloid dendritic cell were lowly infiltrated in cluster 1 (Fig. 8C). The immune checkpoint of SIGLEC15 was highly expressed in cluster 1 (Fig. 8D). The stemness feature analysis showed that cluster 1 had high level of stemness compared to cluster 2 (Fig. 8E). Drug sensitively analysis indicated that the cluster 1 was more sensitively for cisplatin and docetaxel (Fig. 8F). These results indicated that the OSC patients of cluster 1 group might has a more malignant phenotype but more sensitive to cisplatin and docetaxel than cluster 2 group.
The prognostic values for these DRRGs in OSC
Moreover, we download the prognostic profiles from TCGA database in Fig. 5. The survival analysis showed that ORC3/6, MCM3/6, PRIM1/2, POLD2/3, RFC4, RNASEH2A and FEN1 were positively correlated with prognosis in OSC patients (Fig. 9).
Identification of clinical outcomes in OSC based on these DRRGs
For further confirming the clinical outcomes based on these DRRGs in OSC patients, we utilized these 43 DRRGs to construct the prognostic model (lambda.min = 0.0493). The Riskscore=(-0.0277)*PRIM2+(-0.0949)*ORC3+(0.0395)*POLD1+(-0.1048)*POLD2+(-0.0244)*MCM3+(0.0766)*RPA2+(-0.11)*GMNN+(0.0558)*RAD52 (Fig. 10A-B). Then, these OSC patients were divided into high or low risk group via the median risk score (Fig. 10C). The survival analysis showed that the survival time and rate were significantly decreased in high risk group OSC patients compared to low risk OSC patients (Fig. 10D). The ROC curve value was 0.644, 0.631 and 0.6624, respectively, in AUCs at one, two, and three years (Fig. 10E). These results indicated that this prognostic model based on DRRGs had a significant prognostic values in survival monitoring. Furthermore, we confirmed the correlation between risk score and the expression levels of multiple immune cell types in OSC. The result showed that the level of CD8 T, NK, and other uncharacterized cell was decreased, as the risk score increased, but the expression of macrophage was increased, as the risk score increased (Fig. 10F).
Validation of hub DRRGs and AARGs in OSC
Then, we confirmed the DEGs in GSE20489 (Fig. 11A&B). The KEGG analysis indicated that these DEGs were enriched in herpes simplex virus 1 infection, amyotrophic lateral sclerosis, Alzheimer disease, huntington disease, autophagy and T cell receptor signaling pathway (Fig. 11C). GO enrichment showed that these DEGs were enriched in neutrophil activation involved in immune response, neutrophil degranulation, RNA splicing, RNA catabolic process, and proteasome-mediated ubiquitin-dependent protein catabolic process (Fig. 11D). We used Venn analysis found four key gene based on hub DRRGs with prognosis values and hub AARGs, which indicated that the levels of MCM3 and RPA2 were both obviously increased in OSC blood samples based on exoRBase database (Fig. 11E). Moreover, the expression of MCM3 was significantly enhanced in the OSC blood samples compared to heathy blood samples (Fig. 11F), which indicated MCM3 might be a key protein to promote OSC progression by alcohol addiction.
MCM3 might facilitate OC cell DNA replication and proliferation by EVs
We further utilized CCLE database to confirm the level of MCM3 in multiple OSC cancer cell lines (Fig. 11G). We constructed MCM3 knockdown A2780 cell lines and detected by western blot (Fig. 11H). MTT analysis indicated MCM3 inhibiting with MCM3 shRNA#1 and #2 could significantly inhibit the proliferation ability for A2780 cell (Fig. 11I). EdU analysis showed that MCM3 knockdown could significantly reduce the DNA replication level (Fig. 11J). Taken together, these results indicated that alcohol might be a key factor in promoting OSC cell proliferation and DNA replication by upregulating MCM3 expression.